1. Field of the Invention
This invention relates to a cleaning resin composition used for cleaning the inside of various molding machines.
More particularly it relates to a cleaning resin composition having definite quantities of a polystyrene resin, a neutral salt of an alkylbenzenesulfonic acid, an inorganic filler and a water-repellent compound, blended with a high density polyethylene resin having a high viscoelasticity when melted and a narrow molecular weight distribution, and a cleaning resin composition having a low molecular weight polyethylene wax, a neutral salt of an alkylbenzenesulfonic acid and an inorganic filler, blended with a high density polyethylene resin having a high viscoelasticity when melted and a narrow molecular weight distribution.
2. Description of the Related Art
In the field of mold processing of plastics, production of more grades in smaller quantities has been intended. Further, due to the creation of high-performance engineering plastics, the frequency of color exchange or resin exchange inside molding machines has rapidly increased.
Heretofore, at the time of such color exchange or resin exchange, in order to remove contaminants caused by the preceding resin inside the molding machine, the following processes have been employed:
a process of drawing out the contaminated screw inside the molding machine, followed by brushing the screw or the inner wall of the cylinder to thereby clean them, or a process of flowing a colorless resin as a cleaning resin through the inside of the cylinder to clean the screw together with the cylinder, without drawing out the screw.
However, both of these processes require a long time to completely clean the screw and the inside of the molding machine, and in the case of co-cleaning, a large quantity of cleaning resin is required resulting in a large loss in economical and time aspects.
Thus, in order to solve such problems, various cleaning agents for cleaning the inside of molding machines have been developed.
For example, a cleaning agent composed mainly of an acrylic resin, a cleaning agent obtained by blending a surfactant with a thermoplastic resin (Japanese patent application laid-open No. Sho 59-124999), a cleaning agent obtained by blending a surfactant and a lubricant such as a metal salt of stearic acid with a thermoplastic resin (Japanese patent application laid-open No. Sho 58-149998) and a composition obtained by blending a sodium alkylbenzenesulfonate, talc, zinc stearate, etc. with a linear, low density polyethylene (Japanese patent application laid-open No. Sho 60-139411) have been proposed.
However, in the case of the cleaning agent composed mainly of an acrylic resin, since the acrylic resin has a high melt viscosity, a high load is applied to the molding machine at the time of cleaning and also when the temperature inside the molding machine is raised in order to lower the melt viscosity, there is a drawback that the acrylic resin is susceptible to thermal decomposition.
Further, there are drawbacks that operations are troublesome and time consuming. For example, before the cleaning agent is used, the die, metal gauze, etc. of the molding machine have to be removed, and further if the cleaning agent remains inside the molding machine after completion of the cleaning, the remaining cleaning agent mixes in the succeeding molded product so that the agent in the form of foreign matter deteriorates the appearance or the physical properties of the molded product.
Further, in the cases of a cleaning agent obtained by blending a surfactant with a thermoplastic resin and a cleaning agent obtained by further blending a metal stearate, etc. therewith, when the service temperature of these cleaning agents reaches about 250.degree. C. or higher, a gas is generated from decomposition of the cleaning agents so that it has a bad effect upon the operational environment and at the same time, the cleaning effect of the cleaning agent is still insufficient. Further, in the case of the cleaning agent obtained by blending a sodium alkylbenzenesulfonate, talc, etc. with a linear low density polyethylene, since the agent has a low viscoelasticity when melted inside the molding machine, the capability of removing the preceding resin i.e., the cleanability is low, and in the case where the quantity of the inorganic filler blended is large, the cleaning agent itself is liable to remain on the inside wall of the molding machine so that in order to remove the remaining cleaning agent, a large quantity of the cleaning resin has to be used.
Further, the present inventors have previously proposed a thermoplastic resin composition obtained by blending a neutral salt of an alkylbenzenesulfonic acid and a water-repellent compound with a thermoplastic resin (Japanese patent application laid-open No. Sho 62-195045), but a cleaning agent having a further superior cleanability has been desired.